Mechanical strain is a powerful stimulus for shape and size remodeling of cardiac myocytes in normal and pathological situations. Indeed, the major change in shape that precedes heart failure in humans is progression to cellular elongation in dilated cardiomyopathy. The overall objective of this project is to test the hypothesis that longitudinal mechanical strain regulates cell lengthening by differential phosphorylation of focal adhesion kinase (FAK) at the costamere leading to differential actin capping by CapZ at the Z-disc and thin filament addition. The Specific Aims are: Aim #1: To determine the mechanisms of anisotropic Rho family G protein phosphorylation leading to myocyte elongation. We define the subcellular events responsible for strain-induced PKCE signaling using the PKCE-over expressing (OE) mouse, and aligned 3D cultured neonatal rat ventricular myocytes (NRVM) subjected to sudden static strain as model systems. Aim #2: To test the hypothesis that PKC-dependent FAK serine phosphorylation is required for the costameric mechanosensory apparatus to detect longitudinal strain. We examine the PKC dependence of FAK serine phosphorylation in response to longitudinal vs. transverse strain in 3D NRVM cultures. Aim #3: To determine whether elongating myocytes have altered CapZ phosphorylation. We determine whether CapZ phosphorylations in normal mice differ from ventricular myocytes that are lengthening and whether there is differential CapZ phosphorylation in response to anisotropic mechanical inputs to NRVM aligned 3D culture. Aim #4: To test the hypothesis that CapZ phosphorylation and PIP2 binding alter actin capping and are required for length remodeling. We measure actin-capping dynamics of green fluorescent tagged-CapZ to determine the effect of anisotropic mechanical stimuli. We determine the mechanism of cell length remodeling by regulation of CapZ binding via phosphorylation, PIP2 and other CapZ partnering proteins. In these experiments, we use validated conditions of normal myocyte lengthening and challenge these processes with specific molecular interventions to determine the mechanisms of length remodeling.